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Introduction: In this and the next Basic Physiology chapter, we discuss in more details two types of cells in the body that demonstrate several basic physiological principles that are very useful to know and to understand before studying specific organ systems. These are a) the nerve cells and b) the muscle cells. In this and the next pages, we will concentrate on the physiology of the nerve cells.
A. What is a nerve cell?
4.
A nerve cell, like any other living cells, has a body (called ‘soma’), which contains the usual cellular components such as a nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and a plasma membrane (see A.2.1. Structure of the cell).
But, typical for a nerve cell, are the following three components:
- dendrites
- axon
- pre-synaptic terminals
The dendrites are folds of the cell body that extend into the extracellular space, relatively short in length. Their function is to pick up a signal from another nerve cell.
Typical of a nerve cell is that it has many dendrites (10-100) and many terminals (100-1000) but only one (or a few) axon.
In this diagram, you can see several pre-synaptic terminals (from other neurons) close to the membrane of a few dendrites. It is also possible for these pre-synaptic terminals to get close to the membrane of the soma of the nerve cell. These terminals are indicated in yellow.
Note that there is always a cleft (a small space) between the pre-synaptic terminal and the plasma membrane of the dendrite or the soma.
4.
In general, there are three different types of nerve cells in the body:
- sensory neurons
- motor neurons
- inter neurons
Sensory neurons are sensitive to stimuli such as touch, temperature, sound or light and send their signals to the brain.
Motor neurons receive signals from the brain and stimulate muscles to contract.
Inter neurons are nerve cells that connect to other nerve cells, as in the brain or in the spinal cord.
